This invention relates to a width detection method and a width detection apparatus for detecting the width of a record medium on which information is recorded by a recording head, and a record apparatus including the width detection apparatus.
Generally, a large printer, one of record apparatus in related arts, includes a paper feed section for supplying record roll paper, for example, as a record medium, a record section for recording information on supplied roll paper, and a paper ejection section for ejecting the roll paper with information recorded, disposed in this order from top to bottom. To use such a large printer, for example, an ink jet printer, the user stores roll paper in the paper feed section and draws out the leading edge of the roll paper. The user passes the leading edge of the roll paper through the top of a flat paper feed guide serving as a paper transport face and sandwiches the leading edge between a paper feed roller and a driven roller and starts the ink jet printer.
Then, the ink jet printer rotates the paper feed roller for delivering the roll paper onto a flat platen serving as a paper transport guide face and ejects ink droplets from nozzle openings of a recording head for recording information on the roll paper while moving a carriage on which the recording head is mounted in the width direction of the roll paper. The ink jet printer rotates a paper ejection roller for ejecting the roll paper to a paper receptacle through the top of a flat paper ejection guide serving as a paper transport face.
A paper width detection apparatus is disposed in such a large ink jet printer because the flexibility of the width of available roll paper is wide. The paper width detection apparatus detects the width of roll paper by detecting paper while moving a paper detection sensor mounted on a carriage in the width direction of the roll paper. FIG. 23 is a block diagram to show a paper width detection apparatus 1 in a related art. This paper width detection apparatus 1 includes an encoder 2, a photointerrupter 3, a paper detection sensor 4, head position determination means 5, an A/D converter 6, a CPU 7, and memory 8.
The encoder 2 is disposed in the printer main unit and the photointerrupter 3 is disposed on a carriage 9 for generating a pulse signal PLS when the photointerrupter 3 crosses a slit of the encoder 2. The paper detection sensor 4 applies light, for example, detects the reflected light amounts on the roll paper surface and the platen surface (reflected light amount on the roll paper surface>reflected light amount on the platen surface) and the contrast between the edge of the roll paper and the platen surface, and generates a detection signal PDA. The head position determination means 5 determines the position of the recording head based on the pulse signal PLS from the photointerrupter 3 and generates a head position signal HPS.
The A/D converter 6 converts the analog detection signal PDA from the paper detection sensor 4 into a digital detection signal PDD. The CPU 7 stores the head position signal HPS from the head position determination means 5 in the memory 8 based on the detection signal PDD from the A/D converter 6, and computes the roll paper width based on the head position signal HPS.
The roll paper width detection operation in the configuration will be discussed with reference to the block diagram of FIG. 23, a time chart of FIG. 24, and a flowchart of FIG. 25. The head position determination means 5 determines the position of the recording head based on a pulse signal PLS of a 1/180 inch period sent from the photointerrupter 3 and generates a head position signal HPS. The CPU 7 reads the head position signal HPS from the head position determination means 5 in a shorter period than the pulse interval (step S1). When determining that the head position signal HPS changes (step S2), the CPU 7 sends a conversion start command CSS of an analog detection signal PDA to the A/D converter 6.
Upon reception of the conversion start command CSS of an analog detection signal PDA from the CPU 7, the A/D converter 6 starts processing of converting the analog detection signal PDA sent from the paper detection sensor 4 into a digital detection signal PDD. Upon completion of converting the analog signal into the digital detection signal PDD, the A/D converter 6 generates a conversion end interrupt signal CES and sends the signal CES to the CPU 7.
The CPU 7 reads the detection signal PDD from the A/D converter 6 (step S3) with the conversion end interrupt signal CES from the A/D converter 6 received at the pulse interval as a trigger, and determines whether or not change of the detection signal PDD exceeding a predetermined threshold value occurs (step S4). When determining that change of the detection signal PDD exceeding the predetermined threshold value occurs, the CPU 7 stores the head position signal HPS in the memory 8 (step S5). The CPU 7 reads the head position signals HPS when the detection signal PDD exceeds the predetermined threshold value and the detection signal PDD falls below the predetermined threshold value, namely, the head position signals HPS of both end parts of the roll paper from the memory 8, and computes the roll paper width (patent document 1: JP-A-2002-103721).
A business-grade ink jet printer handles various paper types and can handle thin paper, etc., that cannot be picked up by a paper feed mechanism of a consumer ink jet printer (auto sheet feeder (ASF)). In roll paper not transported in an intimate contact state with a platen like thin paper, moderate output change is produced as the paper detection sensor 4 of the paper width detection apparatus in the related art described above crosses the boundary between the edge of roll paper and the platen surface, and it is difficult to accurately find the roll paper width by the method of determining whether or not change of exceeding the predetermined threshold value and change of falling below the predetermined threshold value occur as described above.